Two common display modes for a multipoint video conference are video switching and continuous presence (CP) modes. A multipoint conference is a conference having three or more conferees. In a video switching mode, during a certain period, a conferee can see one other conferee, typically the participant who is the current speaker. The display on the endpoint of the current speaker may present the video image of the previous speaker, for example. In continues presence (CP) mode a conferee can see a composition of a plurality of video images, each located in a segment on the screen. Each segment may be the same size or the segments may have different sizes, for example, with the current speaker displayed in the biggest segment and the other conferees displayed in smaller segments. During the conference the displayed conferees may change frequently according to the dynamic of the conferencing session. Each image may appear different from the others. The appearance of the image can be affected by one or more parameters such as but not limited to brightness, color, sharpness, etc.
The conferees in a multipoint videoconference are typically located at different sites, each having a camera that may be adjusted and/or set up differently than the other sites. The sites may have different brightness conditions and the conferees may be located in environments of different brightness. As such, the video images of different conferees may have different brightness levels. These differences in brightness levels affect a user's experience. For example, in switching mode, a large difference in brightness between the video images of a current speaker compared to the previous speaker can be unpleasant for a user because the user requires more time to get used to the image of the each new current speaker. In a CP mode, large differences in the brightness between the endpoints cause difficulties in finding a display setting such that a user can easily see all of the displayed conferees. The user's vision may adapt to the brighter segments and such that the user may not see details in the darker segments of the display, for example.
Other example of when the brightness of a single image can be improved include situations wherein the brightness conditions and settings of a video camera may be imperfect, creating an image that is either too dark or too bright. These imperfect settings/conditions can degrade details in interesting zones of the image. An example is when a conferee is sitting in a dark area and the image also includes a bright area such as a window on a sunny day.
Accordingly, there is a need in the art for controlling appearance parameters such as the level of the brightness, color, sharpness, etc. of a plurality of video images during a video conference session. Such a method would improve the user's experience.